As outlined in U.S. patent application Ser. No. 444,083, filed Nov. 24, 1982, by John T. Fowler, entitled System for Removably Housing and Aligning Components in a Towed Array, and assigned to the assignee hereof, which application is included herein by reference, for present seismic streamer positioning applications, depth, heading and hence position of an individual sections of seismic streamer cable can be determined and controlled either through the utilization of internally mounted sensors or externally mounted pods, which are clamped onto the seismic streamer at various locations, with the electronics being hard-wired, or in the case of pods, being battery operated and inductively coupled through the streamer casing to cables within the streamer. Examples of the pod type systems include U.S. Pat. Nos. 3,931,608; 3,611,975; 3,704,681; 3,673,556; 3,648,642; and 3,531,761. The mounting of sensing devices wholly within the streamer has the advantage that the electronics are contained wholly within the stream free from damage and, unlike pods, need not be removed upon reeling in on the drum used to store the cable. Examples of these types of systems are described in U.S. Pat. Nos. 4,160,299 and 3,909,774.
In the above-noted patent application, a system for internally housing electronics in an adapter module is described which includes a breech-loaded adapter module which is connected either in a streamer section between adajacent streamer segments or between opposing ends of seismic streamer sections, with a cartridge carrying the electronics, sensors, and/or other components being forced into the breech of the adapter module by an over-the-center lever action cartridge retention system.
The cartridge mounted in the breech is aligned by the sidewalls of the breech to the longitudinal axis of the module, with the module in turn being aligned to the longitudinal axis represented by one of the strain member. Other strained members running through and carried by the module by clamping the module to the strain members are loosely carried in and run through the adapter module, with the result being that the alignment of the sensor within the cartridge is keyed and uniquely determined by one and only one of the strain members. Were the housing clamped to two or more strain members, differential forces produced by the clamped strain members would contort the adapter module housing, thereby causing a misalignment between the longitudinal axis of the cartridge and the strain members.
Not only is such a cartridge useful for carrying various electronics useful in seismic exploration, the cartridge is also useful to carry compressed air or gas in the form of a CO.sub.2 cartridge such that a broken stream cable may be recovered by the puncturing of the CO.sub.2 cartridge, which results in the floating of the cable.
As mentioned in the above patent application, the cartridge is pressed to one end of the breech by an over-the-center locking mechanism. A number of connector pins are provided in a connector at the end of the breech to which the cartridge is moved by the lever-actuated locking mechanism. This connects the cartridge which is inserted into the breech to other electronics which may be carried within the adapter module or to the cables within the streamer. In order to accomplish such a connection, a connector is provided at the far end of the breech.
The advantages of the aforementioned adapter module are first that with the cartridge flush with the outer casing of the module, no flow anomalies are introduced, such as the flow anomolies introduced by the aforementioned pods. Secondly, unlike pods which must be removed when deploying or reeling in the cable, the cartridges need not be removed during cable pay-out or retrieval. Thirdly, the easy removability of the cartridge permits access to a damaged, broken or malfunctioning electrical or other unit without either invasion of the sealed streamer section or the removal of the pods.
As noted in the above patent application, with respect to miniaturization, depth sensors and heading sensors can now be made to a maximum one inch diameter, thereby permitting their mounting in a suitably small cartridge. The cartridge system provides a rigid short streamer section which is guaranteed to be parallel to one of the three strain members, thereby providing, at least for compasses, that the control axis is perfectly parallel to the axis of the streamer. It should be noted that the housing of the above patent application allows strain members of nonmagnetic material to be run through the housing. This provides for ready compensation since an identical housing and strain member can be fixtured at the factory and a cartridge introduced into the breech of the adapter module for compensation purposes. Since both adapter modules and strain members are identical, inserting a calibrated cartridge in the field does not alter the pre-alignment calibration. Finally, the aforementioned adapter module may be placed in active acoustic sections while still providing accessiblity for calibration repair. This has the advantage of not breaking the spacing of acoustic arrays of hydrophones, resulting in a mathematically simpler model.
While the over-the-center latch system described above is satisfactory for mounting cartridges within an adapter module, the over-the-center latch system is somewhat mechanically complicated, expensive to manufacture, and results in the cartridge being exposed to severe mechanical forces when wound on the storage drum or when travelling through the fair-lead or idler pulley at the stern of the boat during pay-out or retrieval.